Got a 05 xc70, starter won't work and click comes from box next to fuse box in boot, any ideas welcome

 

normally a click when engaging the starter comes from the solenoid which is part of the starter motor (it throws out the gear that engages the fly wheel). Anything else that clicks (say much more subtle) is probably a relay that is engaging with the key position such as the fuel pump relay. When you say the starter won't work - do you mean you turn the key and the engine doesn't even crack or does it crank the engine over but it doesn't fire up. Assume it doesn't crank, I'd start by testing battery voltage and perhaps try to start with a jump. Next I'd inspect the battery terminals and cables. On some cars the positive cable has a fuse built into it so that may be tested as well. After that you may need to get creative like testing for the key signaling the starter motor, testing if the large terminal on the motor is getting 12V, touching 12v directly to the starter etc. That may be best left to a shop but you can certainly do some tests with a volt/ohm meter and some inspection of the terminals/cables. When inspecting the starter cable, look for any bubbled or melted insulation (a sign of corrosion inside the cable).